As the federal government closes in on its legal debt limit, the U.S. Treasury is dusting off its book of so-called extraordinary measures — moves that will buy it a few extra months to finance Social Security, military salaries and other payments.

The U.S. was about $67 billion under the $16.394 trillion debt ceiling as of Friday. That’s small change in a world of trillion-dollar deficits and billions in monthly borrowing.

Treasury expects to bump up against the cap, which is set by Congress, very near the end of this month. Lawmakers may not raise it before then — the debt limit has become entangled in fiscal cliff talks. The White House wants to be able to raise the debt ceiling without political drama, though Republicans see their authority over the cap as a crucial bargaining chip to extract spending cuts from the Obama administration.

So, perhaps a week or two before it would go over the top, Treasury is likely to start taking steps that will hold off default until about mid-February or early March.

The play book includes:

–Suspending sales of State and Local Government Series Treasury securities–special-purpose Treasurys known as Slugs that state and local governments use to comply with tax rules. The move doesn’t increase headroom under the ceiling, but it stops Treasury from piling on new public debt.

–Redemption of existing and suspension of new investments in the Civil Service Retirement and Disability Fund after determining that a “debt issuance suspension period” exists. The action allows the government to redeem Treasurys held by the fund–last time around that worked out to about $12 billion over two months. By law, the fund must be made whole once the debt limit is increased.

–Suspending reinvestment in the Government Securities Investment Fund, or G Fund, a money-market defined-contribution retirement fund for federal employees. Federal employees wouldn’t be affected by the action–Treasury is required to replenish the fund. The maneuver bought Treasury about $130 billion in headroom last year.

–Limiting investments in the exchange-stabilization fund, a reserve account related to foreign-exchange holdings. The government has about $23 billion in securities in the fund.

“Once these steps have been taken, no remaining legal and prudent measures would be available to create additional headroom under the debt limit, and the United States would begin to default on its obligations,” Treasury Secretary Timothy Geithner told lawmakers last year.

Treasury never has said exactly what it would do if it breaches the limit.

Treasury’s Office of the Inspector General this summer reported that the department considered asset sales, across-the-board payment reductions, prioritizing payments and delaying payments–and concluded that none would “protect the full faith and credit of the U.S., the American economy, or individual citizens from very serious harm.”

As a last resort, Treasury officials concluded that delaying payments would be the least harmful option, the report said.

During the summer of 2011, the prospect of default undermined confidence, forced the government to pay additional interest costs and led Standard & Poor’s to strip the U.S. government of its top-notch debt rating.

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